Ethylene polymer fiber made from ethylene polymer blends

ABSTRACT

Fibers made from formulated ethylene polymer compositions are disclosed. The ethylene polymer compositions have at least one homogeneously branched linear ethylene/α-olefin interpolymer and at least one heterogeneously branched ethylene polymer. The homogeneously branched linear ethylene/α-olefin interpolymer has a density from about 0.905 to about 0.92 g/cm3 and a slope of strain hardening coefficient greater than or equal to about 1.3.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Rule 1.62 continuation application of applicationSer. No. 08/475,737, filed Jun. 7, 1995, now abandoned, which was acontinuation-in-part application of application Ser. No. 08/378,998,filed Jan. 27, 1995, now abandoned, which was a Rule 1.62 continuationapplication of application Ser. No. 08/054,379, filed Apr. 28, 1993, nowabandoned, which was a continuation-in-part application of Ser. No.07/776,130, filed Oct. 15, 1991, now issued U.S. Pat. No. 5,272, 236,the disclosures of each of which is incorporated herein in theirentirety by reference. This application is also related to issuedapplication Ser. No. 07/939,281, now U.S. Pat. No. 5,278,272, filed Sep.2, 1992; pending application Ser. No. 08/544,497, filed Oct. 18, 1995,which is a continuation application of application Ser. No. 08/378,998,filed Jan. 27, 1995, now abandoned, which was a continuation applicationof application Ser. No. 08/054,379, filed Apr. 28, 1993, now abandoned;and pending application Ser. No. 08/501,527, filed Aug. 2, 1995, whichis a continuation of Ser. No. 08/010,958, filed Jan. 29, 1993, nowabandoned; the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to compositions comprising specificethylene/α-olefin polymer blends. The polymer blends preferablycomprise:

(A) at least one homogeneously branched substantially linearethylene/α-olefin interpolymer having specific processingcharacteristics, blended together with

(B) a heterogeneously branched ethylene polymer.

Such compositions are particularly useful in film applications (e.g.,high strength thin gauge packaging film or heat sealable packagingfilm).

BACKGROUND OF THE INVENTION

Thin film products fabricated from linear low density polyethylene(LLDPE) and/or high density polyethylene (HDPE) are widely used forpackaging applications such as merchandise bags, grocery sacks, andindustrial liners. For these applications, films with high tensilestrength, as well as high impact strength, are desired because filmproducers can down gauge their film products and still retain packagingperformance.

Previous attempts were made to optimize film tensile strength and yieldstrength by blending various heterogeneous polymers together ontheoretical basis. While such blends exhibited a synergistic response toincrease the film yield strength, the film impact strength followed therule of mixing, often resulting in a “destructive synergism” (i.e., thefilm impact strength was actually lower than film made from one of thetwo components used to make the blend).

For example, it is known that while improved modulus linear polyethyleneresin can be produced by blending high density polyethylene with a verylow density polyethylene (VLDPE), the impact strength of the resin blendfollows the rule of mixing.

There is a continuing need to develop polymers which can be formed intofabricated articles (e.g., film) having these combinations of properties(e.g., improved modulus, yield strength, impact strength and tearstrength). The need is especially great for polymers which can be madeinto film which can also be down gauged without loss of strengthproperties, resulting in savings for film manufacturers and consumers,as well as protecting the environment by source reduction.

Surprisingly, we have now discovered that film can have synergisticallyenhanced physical properties, when the film is made from a blend of atleast one homogeneously branched ethylene/α-olefin interpolymer and aheterogeneously branched ethylene/α-olefin interpolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relationship between the density and the slope ofstrain hardening coefficient for homogeneously branched substantiallylinear ethylene/α-olefin interpolymers used in the compositionsdisclosed herein, in comparison with a heterogeneously branchedethylene/α-olefin copolymer.

FIG. 2 shows the short chain branching distribution (as measured byanalytical temperature rising elution fractionation (ATREF)) for ahomogeneously branched substantially linear ethylene/1-octene copolymerused in the invention, in comparison with DowleXx™ 2045 (aheterogeneously branched ethylene/1-octene copolymer made by The DowChemical Company).

SUMMARY OF THE INVENTION

Formulated ethylene/α-olefin compositions have now been discovered tohave improved physical and mechanical strength and are useful in makingfabricated articles. Films made from these novel compositions exhibitsurprisingly good impact and tensile properties, and an especially goodcombination of modulus, yield, ultimate tensile, and toughness (e.g,Dart impact).

The compositions comprise from about (A) 10 percent (by weight of thetotal composition) to about 95 percent (by weight of the totalcomposition) of:

at least one homogeneously branched substantially linearethylene/α-olefin interpolymer having:

(i) a density from about 0.905 grams/cubic centimeter (g/cm³) to about0.92 g/cm³,

(ii) a molecular weight distribution (M_(w)/M_(n)) from about 1.8 toabout 2.8,

(iii) a melt index (I₂) from about 0.001 grams/10 minutes (g/10 min) toabout 10 g/10 min,

(iv) no linear polymer fraction, and

(v) a single melting peak as measured using differential scanningcalorimetry; and

(B) at least one heterogeneously branched ethylene polymer having adensity from about 0.93 g/cm³ to about 0.965 g/cm³.

In another aspect, the compositions comprise from about 10 percent (byweight of the total composition) to about 95 percent (by weight of thetotal composition) of:

(A) at least one homogeneously branched linear ethylene/α-olefininterpolymer having:

(i) a density from about 0.905 grams/cubic centimeter (g/cm³) to about0.92 g/cm³,

(ii) a molecular weight distribution (M_(w)/M_(n)) from about 1.8 toabout 2.8,

(iii) a melt index (I2) from about 0.001 grams/10 minutes (g/10 min) toabout 10 g/10 min,

(iv) no linear polymer fraction, and

(v) a single melting peak as measured using differential scanningcalorimetry; and

(B) at least one heterogeneously branched ethylene polymer having adensity from about 0.93 g/cm³ to about 0.965 g/cm³.

Preferably, both the homogeneously branched substantially linearethylene/α-olefin interpolymer and the homogeneously branched linearethylene/α-olefin interpolymer each have a slope of strain hardeningcoefficient greater than or equal to about 1.3.

DETAILED DESCRIPTION OF THE INVENTION

The homogeneously branched ethylene/α-olefin interpolymer is preferablya homogeneously branched substantially linear ethylene/α-olefininterpolymer as described in pending U.S. Ser. No. 07/776,130 now U.S.Pat. No. 5,272,236. The homogeneously branched ethylene/α-olefininterpolymer can also be a linear ethylene/α-olefin interpolymer asdescribed in U.S. Pat. No. 3,645,992 (Elston), the disclosure of whichis incorporated herein by reference.

The substantially linear ethylene/α-olefin interpolymers are not“linear” polymers in the traditional sense of the term, as used todescribe linear low density polyethylene (e.g., Ziegler polymerizedlinear low density polyethylene (LLDPE)), nor are they highly branchedpolymers, as used to describe low density polyethylene (LDPE).

The substantially linear ethylene/α-olefin interpolymers of the presentinvention are herein defined as in copending application Ser. No.07/776,130 now U.S. Pat. No. 5,272,236 and in copending applicationentitled “Elastic Substantially Linear Olefin Polymers” filed Sep.2,1992 in the names of Shih-Yaw Lai, George W. Knight, John R. Wilsonand James C. Stevens.

The homogeneously branched ethylene/α-olefin interpolymers useful forforming the compositions described herein are those in which thecomonomer is randomly distributed within a given interpolymer moleculeand wherein substantially all of the interpolymer molecules have thesame ethylene/comonomer ratio within that interpolymer. The homogenietyof the interpolymers is typically described by the SCBDI (Short ChainBranch Distribution Index) or CDBI (Composition Distribution BranchIndex) and is defined as the weight percent of the polymer moleculeshaving a comonomer content within 50 percent of the median total molarcomonomer content. The CDBI of a polymer is readily calculated from dataobtained from techniques known in the art, such as, for example,temperature rising elution fractionation (abbreviated herein as “TREF”)as described, for example, in Wild et al, Journal of Polymer Science,Poly. Phys. Ed., Vol. 20, p. 441 (1982), in U.S. Pat. No. 4,798,081(Hazlitt et al.), or in U.S. Pat. No. 5,089,321 (Chum et al.) thedisclosures of all of which are incorporated herein by reference. TheSCBDI or CDBI for the linear and for the substantially linear olefinpolymers of the present invention is preferably greater than about 30percent, especially greater than about 50 percent. The homogeneousethylene/α-olefin polymers used in this invention essentially lack ameasurable “high density” fraction as measured by the TREF technique(i.e., the homogeneously branched ethylene/α-olefin polymers do notcontain a polymer fraction with a degree of branching less than or equalto 2 methyls/1000 carbons). The homogeneously branched ethylene/α-olefinpolymers also do not contain any highly short chain branched fraction(i.e., the homogeneously branched ethylene/α-olefin polymers do notcontain a polymer fraction with a degree of branching equal to or morethan about 30 methyls/1000 carbons).

The substantially linear ethylene/α-olefin interpolymers for use in thepresent invention typically are interpolymers of ethylene with at leastone C₃-C₂₀ α-olefin and/or C₄-C₁₈ diolefins. Copolymers of ethylene and1-octene are especially preferred. The term “interpolymer” is usedherein to indicate a copolymer, or a terpolymer, or the like. That is,at least one other comonomer is polymerized with ethylene to make theinterpolymer. Ethylene copolymerized with two or more comonomers canalso be used to make the homogeneously branched substantially linearinterpolymers useful in this invention. Preferred comonomers include theC₃-C₂₀ α-olefins, especially propene, isobutylene, 1-butene, 1-hexene,4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, and 1-decene, morepreferably 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene.

The term “linear ethylene/α-olefin interpolymer” means that theinterpolymer does not have long chain branching. That is, the linearethylene/α-olefin interpolymer has an absence of long chain branching,as for example the linear low density polyethylene polymers or linearhigh density polyethylene polymers made using uniform (i.e.,homogeneous) branching distribution polymerization processes (e.g., asdescribed in U.S. Pat. No. 3,645,992 (Elston)) and are those in whichthe comonomer is randomly distributed within a given interpolymermolecule and wherein substantially all of the interpolymer moleculeshave the same ethylene/comonomer ratio within that interpolymer. Theterm “linear ethylene/α-olefin interpolymer” does not refer to highpressure branched (free-radical polymerized) polyethylene which is knownto those skilled in the art to have numerous long chain branches. Thebranching distribution of the homogeneously branched linearethylene/α-olefin interpolymers is the same or substantially the same asthat described for the homogeneously branched substantially linearethylene/α-olefin interpolymers, with the exception that the linearethylene/α-olefin interpolymers do not have any long chain branching.The homogeneously branched linear ethylene/α-olefin interpolymerscomprise ethylene with at least one C₃-C₂₀ α-olefin and/or C₄-C₁₈diolefin. Copolymers of ethylene and 1-octene are especially preferred.Preferred comonomers include the C₃-C₂₀ α-olefins, especially propene,isobutylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-heptene,1-octene, 1-nonene, and 1-decene, more preferably 1-butene, 1-hexene,4-methyl-1-pentene and 1-octene.

Both the homogeneously branched substantially linear and linearethylene/α-olefin interpolymers have a single melting point, as opposedto traditional heterogeneously branched Ziegler polymerizedethylene/α-olefin copolymers having two or more melting points, asdetermined using differential scanning calorimetry (DSC).

The density of the homogeneously branched linear or substantially linearethylene/α-olefin interpolymers (as measured in accordance with ASTMD-792) for use in the present invention is generally from about 0.89g/cm³ to about 0.935 g/cm³, preferably from about 0.905 g/cm³ to about0.925 g/cm³, and especially from about 0.905 g/cm³ to less than about0.92 g/cm³.

The amount of the homogeneously branched linear or substantially linearethylene/α-olefin polymer incorporated into the composition variesdepending upon the heterogeneously branched ethylene polymer to which itis combined. However, about 50 percent (by weight of the totalcomposition) of the homogeneous linear or substantially linearethylene/α-olefin polymer is especially preferred in the novelcompositions disclosed herein.

The molecular weight of the homogeneously branched linear orsubstantially linear ethylene/α-olefin interpolymers for use in thepresent invention is conveniently indicated using a melt indexmeasurement according to ASTM D-1238, Condition 190_C/2.16 kg (formerlyknown as “Condition (E)” and also known as I₂). Melt index is inverselyproportional to the molecular weight of the polymer. Thus, the higherthe molecular weight, the lower the melt index, although therelationship is not linear. The lower melt index limit for thehomogeneously branched linear or substantially linear ethylene/α-olefininterpolymers useful herein is generally about 0.001 grams/10 minutes(g/10 min). The upper melt index limit for the homogeneously branchedlinear or substantially linear ethylene/α-olefin interpolymers is about10 g/10 min, preferably less than about 1 g/10 min, and especially lessthan about 0.5 g/10 min.

Another measurement useful in characterizing the molecular weight of thehomogeneously branched linear or substantially linear ethylene/α-olefininterpolymers is conveniently indicated using a melt index measurementaccording to ASTM D-1238, Condition 190_C/10 kg (formerly known as“Condition (N)” and also known as I₁₀). The ratio of the I₁₀ and I₂ meltindex terms is the melt flow ratio and is designated as I₁₀/I₂.Generally, the I₁₀/I₂ ratio for the homogeneously branched linearethylene/α-olefin interpolymers is about 5.6. For the homogeneouslybranched substantially linear ethylene/α-olefin interpolymers used inthe compositions of the invention, the I₁₀/I₂ ratio indicates the degreeof long chain branching, i.e., the higher the I₁₀/I₂ ratio, the morelong chain branching in the interpolymer. Generally, the I₁₀/I₂ ratio ofthe homogeneously branched substantially linear ethylene/α-olefininterpolymers is at least about 6, preferably at least about 7,especially at least about 8 or above. For the homogeneously branchedsubstantially linear ethylene/α-olefin interpolymers, the higher theI_(10/I) ₂ ratio, the better the processability.

Other additives such as antioxidants (e.g., hindered phenolics (e.g.,Irganox® 1010 made by Ciba Geigy Corp.), phosphites (e.g., Irgafos® 168also made by Ciba Geigy Corp.)), cling additives (e.g., PIB), antiblockadditives, pigments, fillers, and the like can also be included in theformulations, to the extent that they do not interfere with the enhancedformulation properties discovered by Applicants.

Molecular Weight Distribution Determination

The molecular weight distribution of the linear or substantially linearolefin interpolymer product samples is analyzed by gel permeationchromatography (GPC) on a Waters 150C high temperature chromatographicunit equipped with three mixed porosity columns (Polymer Laboratories10³, 10⁴, 10⁵, and 10⁶), operating at a system temperature of 140° C.The solvent is 1,2,4-trichlorobenzene, from which 0.3 percent by weightsolutions of the samples are prepared for injection. The flow rate is1.0 milliliter/minute and the injection size is 200 microliters. Adifferential refractometer is being used as the detector.

The molecular weight determination is deduced by using narrow molecularweight distribution polystyrene standards (from Polymer Laboratories) inconjunction with their elution volumes. The equivalent polyethylenemolecular weights are determined by using appropriate Mark-Houwinkcoefficients for polyethylene and polystyrene (as described by Williamsand Word in Journal of Polymer Science, Polymer Letters, Vol. 6,(621)1968, incorporated herein by reference) to derive the followingequation:

M_(polyethylene)=a*(M_(polystyrene))^(b).

In this equation, a=0.4316 and b=1.0. Weight average molecular weight,M_(w), is calculated in the usual manner according to the followingformula: M_(w)=Σw_(i)* M_(i), where w_(i) and M_(i) are the weightfraction and molecular weight, respectively, of the i^(th) fractioneluting from the GPC column.

For both the homogeneously branched linear and substantially linearethylene/α-olefin polymers, the molecular weight distribution(M_(w)/M_(n)) is preferably from about 1.8 to about 2.8, more preferablyfrom about 1.89 to about 2.2 and especially about 2.

Determination of the Slope of Strain Hardening Coefficient

The slope of strain hardening is measured by compression molding aplaque from the polymer to be tested. Typically, the plaque is molded atabout 177° C. for 4 minutes under almost no pressure and then pressedfor 3 minutes under a pressure of about 200 psi. The plaque is thenallowed to cool at about 8° C./minute while still under 200 psipressure. The molded plaque has a thickness of about 0.005 inches. Theplaque is then cut into a dogbone shaped test piece using a steel ruledie. The test piece is 0.315 inches wide and 1.063 inches long. Thestart of the curved portion of the dogbone shape begins at 0.315 inchesfrom each end of the sample and gently curves (i.e., tapers) to a widthof 0.09 inches. The curve ends at a point 0.118 inches from the start ofthe curve such that the interior portion of the dogbone test piece has awidth of 0.09 inches and a length of 0.197 inches.

The tensile properties of the test sample is tested on an InstronTensile Tester at a crosshead speed of 1 inch/minute. The slope ofstrain hardening is calculated from the resulting tensile curve bydrawing a line parallel to the strain hardening region of the resultingstress/strain curve. The strain hardening region occurs after the samplehas pulled its initial load ((i.e., stress) usually with little or noelongation during the intial load) and after the sample has gone througha slight drawing stage (usually with little or no increase in load, butwith increasing elongation (i.e., strain)). In the strain hardeningregion, the load and the elongation of the sample both continue toincrease. The load increases in the strain hardening region at a muchlower rate than during the intial load region and the elongation alsoincrease, again at a rate lower than that experienced in the drawingregion. FIG. 1 shows the various stages of the stress/strain curve usedto calculate the slope of strain hardening. The slope of the parallelline in the strain hardening region is then determined.

The slope of strain hardening coefficient (SHC) is calculated accordingto the following equation:

SHC=(slope of strain hardening)*(I₂)^(0.25)

where I₂=melt index in grams/10 minutes.

For both the homogeneously branched linear and substantially linearethylene/α-olefin interpolymers used in the invention, the SHC isgreater than about 1.3, preferably greater than about 1.5.

Surprisingly, the slope of strain hardening coefficient reaches amaximum for the linear or the substantially linear ethylene/α-olefinpolymers at a density from about 0.89 g/cm³ to about 0.935 g/cm³.Heterogeneous ethylene/α-olefin polymers, in contrast, do not behave inthe same manner. FIG. 1 graphically depicts the relationship between thedensity of the homogeneously branched substantially linear ethylenepolymers and ethylene/α-olefin polymers as a function of their slope ofstrain hardening coefficient, and includes a heterogenously branchedethylene/1-octene copolymer (polymer W** in Table 1) for comparisonpurposes. Table 1 displays the data of FIG. 1 in tabular form:

TABLE 1 Melt Index (I₂) Density Polymer (g/10 min) (g/cm³) I₁₀/I₂ SHC* A1 0.8564 7.36 0.004 B 1.03 0.8698 7.46 0.45 C 0.57 0.873 7.22 0.54 D1.01 0.8817 7.36 0.89 E 1.06 0.9018 7.61 1.84 F 2.01 0.9041 8.07 2.03 G0.77 0.9047 9.01 1.57 H 9.82 0.9048 7.03 1.67 I 4.78 0.9077 7.18 2.08 J3.13 0.9113 7.67 2.04 K 2.86 0.9139 7.87 2.27 L 1.08 0.9197 8.07 2.24 M0.96 0.9198 9.61 1.93 N 0.99 0.9203 9.09 2.23 O 1.11 0.9204 10.15 1.59 P1.06 0.9205 9.08 2.25 Q 1.12 0.9216 8.94 2.3 R 30.74 0.9217 6.27 2 S31.58 0.94 6.02 0.24 T 0.97 0.9512 12.11 0 U 0.97 0.9533 10.5 0 V 0.920.954 7.39 0 W** 0.8 0.905 8.7 1.02 *SHC = Slope of Strain HardeningCoefficient **A comparative heterogeneously branched ethylene/1-octenecopolymer

The Heterogeneously Branched Ethylene Polymer

The ethylene polymer to be combined with the homogeneousethylene/α-olefin interpolymer is a heterogeneously branched (e.g.,Ziegler polymerized) interpolymer of ethylene with at least one C₃-C₂₀α-olefin (e.g., linear low density polyethylene (LLDPE)).

Heterogeneously branched ethylene/α-olefin interpolymers differ from thehomogeneously branched ethylene/α-olefin interpolymers primarily intheir branching distribution. For example, heterogeneously branchedLLDPE polymers have a distribution of branching, including a highlybranched portion (similar to a very low density polyethylene), a mediumbranched portion (similar to a medium branched polyethylene) and anessentially linear portion (similar to linear homopolymer polyethylene).The amount of each of these fractions varies depending upon the wholepolymer properties desired. For example, linear homopolymer polyethylenehas neither branched nor highly branched fractions, but is linear. Avery low density heterogeneous polyethylene having a density from about0.9 g/cm³ to about 0.915 g/cm³ (such as Attane® copolymers, sold by TheDow Chemical Company and Flexomer® sold by Union Carbide Corporation)has a higher percentage of the highly short chain branched fraction,thus lowering the density of the whole polymer.

Heterogeneously branched LLDPE (such as Dowlex® sold by The Dow ChemicalCompany) has a lower amount of the highly branched fraction, but has agreater amount of the medium branched fraction. FIG. 2 graphicallydepicts the relative amounts of these various fractions (as measuredusing temperature rising elution fractionation) for Dowlex® 2045 (aheterogeneously branched ethylene/1-octene copolymer having a melt index(I₂) of about 1 g/10 min, a density of about 0.92 g/cm³, a melt flowratio (I₁₀/I₂) of about 7.93 and a molecular weight distribution(M_(w)/M_(n)) of about 3.34), as compared with a homogeneously branchedsubstantially linear ethylene/1-octene copolymer having a melt index(I₂) of about 1 g/10 min, a density of about 0.92 g/cm³, a melt flowratio (I₁₀/I₂) of about 10.5 and a molecular weight distribution(M_(w)/M_(n)) of about 2.18. Note that the homogeneously branchedpolymer has a single relatively narrow peak at an elution temperature ofabout 85° C., while the Dowlex® 2045 polymer has a broad branchingdistribution, as represented by the breadth of elution temperatures overwhich the polymer fractions eluted. Dowlex® 2045 also has a distinctpeak at an elution temperature of about 98° C., indicating the “linear”fraction of the whole polymer. Increasing the fraction of the polymerwhich has the beneficial properties, without concommitantly increasingother fractions has not been demonstrated here-to-fore.

Preferably, however, the heterogeneously branched ethylene polymer is aheterogeneously branched Ziegler polymerized ethylene/α-olefininterpolymer having no more than about 10 percent (by weight of thepolymer) of a polymer fraction having a SHC≧1.3.

More preferably, the heterogeneously branched ethylene polymer is acopolymer of ethylene with a C₃-C₂₀ α-olefin, wherein the copolymer has:

(i) a density from about 0.93 g/cm³ to about 0.965 g/cm³,

(ii) a melt index (I₂) from about 0.1 g/10 min to about 500 g/10 min,and

(iii) no more than about 10 percent (by weight of the polymer) of apolymer fraction having a SHC≧1.3.

Even more preferably, the heterogeneously branched polymer will have adensity of at least about 0.935 g/cm³. In particularly preferredembodiments, the heterogeneously branched polymer will have a density ofno more than about 0.960 g/cm³, more preferably no more than about 0.955g/cm³, and most preferably no more than about 0.950 g/cm³.

When the density of the heterogeneously branched interpolymer is no morethan about 0.950 g/cm³, the interpolymer will typically be characterizedby a molecular weight distribution (M_(w)/M_(n)) greater than 3,preferably at least 3.2, and more preferably at least 3.3. Further, whenthe density of the heterogeneously branched interpolymer is no more thanabout 0.950 g/cm³, the SCBDI or CDBI, as defined above, is preferablyless than 30 percent.

The heterogeneously branched ethylene/α-olefin interpolymers and/orcopolymers also have at least two melting peaks as determined usingDifferential Scanning Calorimetry (DSC).

The Formulated Compositions

The compositions disclosed herein can be formed by any convenientmethod, including dry blending the individual components andsubsequently melt mixing or by pre-melt mixing in a separate extruder(e.g., a Banbury mixer, a Haake mixer, a Brabender internal mixer, or atwin screw extruder).

Another technique for making the compositions in-situ is disclosed inpending U.S. Ser. No. 08/010,958, entitled EthyleneInterpolymerizations, which was filed Jan. 29, 1993 in the names ofBrian W. S. Kolthammer and Robert S. Cardwell, the disclosure of whichis incorporated herein in its entirety by reference. U.S. Ser. No.08/010,958 describes, inter alia, interpolymerizations of ethylene andC₃-C₂₀ alpha-olefins using a homogeneous catalyst in at least onereactor and a heterogeneous catalyst in at least one other reactor. Thereactors can be operated sequentially or in parallel.

The compositions can also be made by fractionating a heterogeneousethylene/α-olefin polymer into specific polymer fractions with eachfraction having a narrow composition (i.e., branching) distribution,selecting the fraction having the specified properties (e.g., SHC≧1.3),and blending the selected fraction in the appropriate amounts withanother ethylene polymer. This method is obviously not as economical asthe in-situ interpolymerizations of U.S. Ser. No. 08/010,958, but can beused to obtain the compositions of the invention.

Fabricated Articles Made from the Novel Compositions

Many useful fabricated articles benefit from the novel compositionsdisclosed herein. For example, molding operations can be used to formuseful fabricated articles or parts from the compositions disclosedherein, including various injection molding processes (e.g., thatdescribed in Modern Plastics Encyclopedia/89, Mid October 1988 Issue,Volume 65, Number 11, pp. 264-268, “Introduction to Injection Molding”by H. Randall Parker and on pp. 270-271, “Injection MoldingThermoplastics” by Michael W. Green, the disclosures of which areincorporated herein by reference) and blow molding processes (e.g., thatdescribed in Modern Plastics Encyclopedia/89, Mid October 1988 Issue,Volume 65, Number 11, pp. 217-218, “Extrusion-Blow Molding” byChristopher Irwin, the disclosure of which is incorporated herein byreference), profile extrusion, calandering, pultrusion (e.g., pipes) andthe like. Rotomolded articles can also benefit from the novelcompositions described herein. Rotomolding techniques are well known tothose skilled in the art and include, for example, those described inModern Plastics Encyclopedia/89, Mid October 1988 Issue, Volume 65,Number 11, pp. 296-301, “Rotational Molding” by R. L. Fair, thedisclosure of which is incorporated herein by reference).

Fibers (e.g., staple fibers, melt blown fibers or spunbonded fibers(using, e.g., systems as disclosed in U.S. Pat. Nos. 4,340,563,4,663,220, 4,668,566, or 4,322,027, all of which are incorporated hereinby reference), and gel spun fibers (e.g., the system disclosed in U.S.Pat No. 4,413,110, incorporated herein by reference)), both woven andnonwoven fabrics (e.g., spunlaced fabrics disclosed in U.S. Pat. No.3,485,706, incorporated herein by reference) or structures made fromsuch fibers (including, e.g., blends of these fibers with other fibers,e.g., PET or cotton)) can also be made from the novel compositionsdisclosed herein.

Film and film structures particularly benefit from the novelcompositions described herein and can be made using conventional hotblown film fabrication techniques or other biaxial orientation processessuch as tenter frames or double bubble processes. Conventional hot blownfilm processes are described, for example, in The Encyclopedia ofChemical Technology, Kirk-Othmer, Third Edition, John Wiley & Sons, NewYork, 1981, Vol. 16, pp. 416-417 and Vol. 18, pp. 191-192, thedisclosures of which are incorporated herein by reference. Biaxialorientation film manufacturing process such as described in a “doublebubble” process as in U.S. Pat. No. 3,456,044 (Pahlke), and theprocesses described in U.S. Pat. No. 4,352,849 (Mueller), U.S. Pat. No.4,597,920 (Golike), U.S. Pat. No. 4,820,557 (Warren), U.S. Pat. No.4,837,084 (Warren), U.S. Pat. No. 4,865,902 (Colike et al.), U.S. Pat.No. 4,927,708 (Herran et al.), U.S. Pat. No. 4,952,451 (Mueller), U.S.Pat. No. 4,963,419 (Lustig et al.), and U.S. Pat. No. 5,059,481 (Lustiget al.), the disclosures of each of which are incorporated herein byreference, can also be used to make film structures from the novelcompositions described herein. The film structures can also be made asdescribed in a tenter-frame technique, such as that used for orientedpolypropylene.

Other multi-layer film manufacturing techniques for food packagingapplications are described in Packaging Foods With Plastics, by WilmerA. Jenkins and James P. Harrington (1991), pp.19-27, and in “CoextrusionBasics” by Thomas I. Butler, Film Extrusion Manual: Process, Materials,Properties pp. 31-80 (published by TAPPI Press (1992)) the disclosuresof which are incorporated herein by reference.

The films may be monolayer or multilayer films. The film made from thenovel compositions can also be coextruded with the other layer(s) or thefilm can be laminated onto another layer(s) in a secondary operation,such as that described in Packaging Foods With Plastics, by Wilmer A.Jenkins and James P. Harrington (1991) or that described in “CoextrusionFor Barrier Packaging” by W. J. Schrenk and C. R. Finch, Society ofPlastics Engineers RETEC Proceedings, Jun. 15-17 (1981), pp. 211-229,the disclosure of which is incorporated herein by reference. If amonolayer film is produced via tubular film (i.e., blown filmtechniques) or flat die (i.e., cast film) as described by K. R. Osbornand W. A. Jenkins in “Plastic Films, Technology and PackagingApplications” (Technomic Publishing Co., Inc. (1992)), the disclosure ofwhich is incorporated herein by reference, then the film must go throughan additional post-extrusion step of adhesive or extrusion lamination toother packaging material layers to form a multilayer structure. If thefilm is a coextrusion of two or more layers (also described by Osbornand Jenkins), the film may still be laminated to additional layers ofpackaging materials, depending on the other physical requirements of thefinal film. “Laminations Vs. Coextrusion” by D. Dumbleton (ConvertingMagazine (September 1992), the disclosure of which is incorporatedherein by reference, also discusses lamination versus coextrusion.Monolayer and coextruded films can also go through other post extrusiontechniques, such as a biaxial orientation process.

Extrusion coating is yet another technique for producing multilayer filmstructures using the novel compositions described herein. The novelcompositions comprise at least one layer of the film structure. Similarto cast film, extrusion coating is a flat die technique. A sealant canbe extrusion coated onto a substrate either in the form of a monolayeror a coextruded extrudate.

Generally for a multilayer film structure, the novel compositionsdescribed herein comprise at least one layer of the total multilayerfilm structure. Other layers of the multilayer structure include but arenot limited to barrier layers, and/or tie layers, and/or structurallayers. Various materials can be used for these layers, with some ofthem being used as more than one layer in the same film structure. Someof these materials include: foil, nylon, ethylene/vinyl alcohol (EVOH)copolymers, polyvinylidene chloride (PVDC), polyethylene terepthalate(PET), oriented polypropylene (OPP), ethylene/vinyl acetate (EVA)copolymers, ethylene/acrylic acid (EAA) copolymers, ethylene/methacrylicacid (EMAA) copolymers, LLDPE, HDPE, LDPE, nylon, graft adhesivepolymers (e.g., maleic anhydride grafted polyethylene), and paper.Generally, the multilayer film structures comprise from 2 to about 7layers.

EXAMPLE 1

Seventy five percent (by weight of the total composition) of ahomogeneously branched substantially linear ethylene/1-octene copolymerhaving I₂ of about 1 g/10 min, density of about 0.91 g/cm³, I_(10/I) ₂of about 10, M_(w)/M_(n) of about 2, and SHC of about 1.81 is dryblended and then melt blended with 25 percent (by weight of the totalcomposition) of a heterogeneously branched ethylene/1-octene copolymerhaving I₂ of about 1 g/10 min, density of about 0.935 g/cm³, I_(10/I) ₂of about 7.8, and M_(w)/M_(n) of about 3.4. The heterogeneously branchedethylene/1-octene copolymer has a fraction of about 5 percent (by weightof the heterogeneously branched copolymer) having a SHC≧1.3. The dryblend is tumble blended in a 50 gallon drum for about 1 hour.

The melt blend is produced in a ZSK 30 twin screw extruder (30 mm screwdiameter) and is then fabricated into film. The final blendedcomposition has a density of about 0.919 g/cm³.

The blended composition is then fabricated into blown film having athickness of about 1 mil on an Egan Blown Film Line having a 2 inchdiameter screw, a 3 inch die and at a 2.5 inch blow up ratio (BUR), asdescribed in Table 2. For all film samples in Examples 1, 2, 4, and 6and for comparative examples 3, 5, and 7, the targeted gauge is about 1mil, using a blow-up ratio (BUR) of 2.5:1, a LLDPE screw design is used,a die gap of 70 mils is used, and a lay flat of about 11.875 inches isused.

Film properties are measured and reported in Table 3 with other examplesof the invention and with comparative examples. Dart impact (type A) ofthe films is measured in accordance with ASTM D-1709-85; tensilestrength, yield, toughness, and 2% secant modulus of the films ismeasured in accordance with ASTM D-882; Elmendorf tear (type B) ismeasured in accordance with ASTM D-1922; PPT tear is measured inaccordance with ASTM D-2582; Block is measured in accordance with ASTMD-3354.

Puncture is measured by using an Instron tensiometer Tensile Tester withan integrator, a specimen holder that holds the film sample taut acrossa circular opening, and a rod-like puncturing device with a rounded tip(ball) which is attached to the cross-head of the Instron and impingesperpendicularly onto the film sample. The Instron is set to obtain acrosshead speed of 10 inches/minute and a chart speed (if used) of 10inches/minute. Load range of 50% of the load cell capacity (100 lb. loadfor these tests) should be used. The puncturing device is installed tothe Instron such that the clamping unit is attached to the lower mountand the ball is attached to the upper mount on the crosshead. Six filmspecimens are used (each 6 inches square). The specimen is clamped inthe film holder and the film holder is secured to the mounting bracket.The crosshead travel is set and continues until the specimen breaks.Puncture resistance is defined as the energy to puncture divided by thevolume of the film under test. Puncture resistance (PR) is calculated asfollows:

PR=E/((12)(T)(A))

where

PR=puncture resistance (ft-lbs/in³)

E=energy (inch-lbs)=area under the load displacement curve

12=inches/foot

T=film thickness (inches), and

A=area of the film sample in the clamp=12.56 in².

EXAMPLE 2

Seventy five percent (by weight of the total composition) of ahomogeneously branched substantially linear ethylene/1-octene copolymerhaving I₂ of about 0.5 g/10 min, density of about 0.915 g/cm³, I₁₀/I₂ ofabout 11, M_(w)/M_(n) of about 2.4, and SHC of about 2.265 is dryblended and then melt blended (as described in Example 1) with 25percent (by weight of the total composition) of a heterogeneouslybranched ethylene/1-octene copolymer having I₂ of about 1 g/10 min,density of about 0.935 g/cm³, I₁₀/I₂ of about 7.8, and M_(w)/m_(n) ofabout 3.4. The heterogeneously branched ethylene/1-octene copolymer hasa fraction of about 5 percent (by weight of the heterogeneously branchedcopolymer) having a SHC≧1.3. The final blended composition has a densityof about 0.92 g/cm³.

Blown film is made as described in Table 2 and film properties aremeasured and reported in Table 3 with other examples of the inventionand with comparative examples.

Comparative Example 3

A heterogeneously branched ethylene/1-octene copolymer having I₂ ofabout 1 g/10 min, density of about 0.92 g/cm³, I₁₀/I₂ of about 7.93, andM_(w)/m_(n) of about 3.34 is made into film as described in Example 1.The heterogeneously branched ethylene/1-octene copolymer has a fractionof about 36 percent (by weight of the heterogeneous copolymer) having aSHC≧1.3. The entire heterogeneous ethylene/1-octene copolymer has a SHCof about 1.5.

Blown film is made as described in Table 2 and film properties aremeasured and reported in Table 3 with other examples of the inventionand with comparative examples.

EXAMPLE 4

Example 4 is an in-situ blend made according to U.S. Ser. No.08/010,958, now abandoned wherein the homogeneously branchedsubstantially linear polymer is made in a first reactor and is anethylene/1-octene copolymer having a melt index (I₂) of about 0.5 g/10min., and a density of about 0.9054 g/cm³, a melt flow ratio (I₁₀/I₂) ofabout 8.27 and a molecular weight distribution (M_(w)/M_(n)) of about1.979 and comprises about 50% (by weight of the total composition). Aheterogeneously branched ethylene/1-octene copolymer is made in a secondreactor operated sequentially with the first reactor and has a meltindex (I₂) of about 1.5 g/10 min., and a density of about 0.944 g/cm³and comprises the remaining 50% (by weight of the total composition).The total composition has a melt index (I₂) of about 1 g/10 min., adensity of about 0.9248 g/cm³, a melt flow ratio (I₁₀/I₂) of about 7.22and a molecular weight distribution (M_(w)/M_(n)) of about 2.641. Thiscomposition is made into blown film as described in Table 2 and theresultant film properties are reported in Table 3.

Comparative Example 5

Comparative Example 5 is an ethylene/1-octene copolymer made accordingto U.S. Ser. No. 07/773,375, filed Oct. 7, 1991, now U.S. Pat. No.5,250,612 the disclosure of which is incorporated herein by reference.About 15% (by weight of the total composition) is made in a firstreactor, with the remaining portion of the composition polymerized in asecond sequentially operated reactor. Both reactors utilize Ziegler typecatalysts and make heterogeneously branched polymers. The totalcomposition has a melt index (I₂) of about 0.56 g/10 min., a density ofabout 0.9256 g/cm³, a melt flow ratio (I₁₀/I₂) of about 9.5 and amolecular weight distribution (M_(w)/M_(n)) of about 4.35. Thiscomposition is also made into blown film as described in Table 2 and theresultant film properties are reported in Table 3.

EXAMPLE 6

Example 6 is an in-situ blend made according to U.S. Ser. No.08/010,958, now abandoned wherein the homogeneously branchedsubstantially linear polymer is made in a first reactor and is anethylene/1-octene coplymer having a fractional melt index (I₂), adensity of about 0.906 g/cm³, a melt flow ratio (I₁₀/I₂) of about 8-10and a molecular weight distribution (M_(w)/M_(n)) of about 2.2 andcomprises about 43% (by weight of the total composition). A secondheterogeneously branched ethylene/1-octene copolymer is made in a secondreactor operated sequentially with the first reactor and has a meltindex (I₂) of about 0.85 g/10 minutes, a density of about 0.938 g/cm³and comprises the remaining 57% (by weight of the total composition).The total composition has a melt index (I₂) of about 0.53 g/10 minutes,a density of about 0.9246 g/cm³, a melt flow ratio (I₁₀/I₂) of about7.83, and a molecular weight distribution (M_(w)/M_(n)) of about 2.8.This composition is made into blown film as described in Table 2 and thefilm properties are reported in Table 3.

Comparative Example 7

Comparative Example 7 is an ethylene/1-octene copolymer made accordingto U.S. Ser. No. 07/773,375, filed Oct. 7, 1991 now U.S. Pat. No.5,250,612, the disclosure of which is incorporated herein by reference.About 25% (by weight of the total composition) is made in a firstreactor, with the remaining portion of the composition polymerized in asecond sequentially operated reactor. Both reactors utilize Ziegler typecatalysts and make heterogeneously branched polymers. The totalcomposition has a melt index (I₂) of about 0.49 g/10 min., a density ofabout 0.9244 g/cm³, a melt flow ratio (I₁₀/I₂) of about 10 and amolecular weight distribution (M_(w)/M_(n)) Of about 4.78. Thiscomposition is also made into blown film as described in Table 2 and theresultant film properties are reported in Table 3.

Comparative Example 8

Comparative example 8 is a heterogeneously branched ethylene/1-octenecopolymer having a melt index (I₂) of about 1 g/10 minutes, a density ofabout 0.9249 g/cm³, a melt flow ratio (I₁₀/I₂) of about 8 and amolecular weight distrubution (M_(w)/M_(n)) of about 3.5.

Blown film is made as described in Table 2 and film properties aremeasured and reported in Table 3 with other examples of the inventionand comparative examples.

TABLE 2 Comp Comp Comp Comp Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7Ex. 8 Zone 1A (° F.) 300 300 300 300 300 300 300 300 Zone 1B (° F.) 450451 475 474 475 475 475 474 Zone 1C (° F.) 450 450 475 475 475 475 475475 Zone 2A (° F.) 450 450 475 474 475 475 475 475 Zone 2B (° F.) 450450 455 475 475 475 475 475 Zone 2C (° F.) 450 450 475 475 475 475 475475 Zone 3 (° F.) 451 452 474 477 477 476 476 474 Zone 4 (° F.) 450 450473 475 475 475 475 475 Zone 5 (° F.) 450 450 475 475 475 475 475 475Melt temp. (° F.) 475 477 515 501 502 499 499 497 Blower Air 47.3 45.757 44.4 86.5 47.6 NA 47.3 temp. (° F.) Chill Water 39 37.6 51.1 38.386.8 40 38.7 40.5 temp. (° F.) Extruder Die 2843 3427 1321 1874 17632883 2525 1952 press. (psi) Nozzle 3.2 4.5 4.38 4.4 4.9 4.6 4.6 4.3press. (in.) Amps 27.3 33.1 37.7 39.9 40.2 50.1 42.6 38.6 Extruder 27.628.8 21.5 23.1 21.1 21.5 22.1 21.7 speed (rpm) Nip Roll 33.1 36.9 3939.8 36.2 37 36 37.8 speed (rpm) Output (lbs/hr) 31 NR* 38.3 39 NR* 3636 36 Frost line 12.5 9 13 12 12 10.5 11 10.5 height (in.) *NR = Notrecorded

TABLE 3 Comp Comp Comp Comp Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7Ex. 8 Yield (MD*) (psi) 1605 1595 1643 2040 2243 1973 1810 1782 Tensile(MD*) (psi) 8522 9525 7444 7794 7931 9325 8455 4928 Toughness (MD*) 16891773 1439 1671 1519 NR NR NR (ft-lbs/in³) Yield (CD**) (psi) 1530 14891706 2267 2407 1997 1809 1832 Tensile (CD**) (psi) 6252 7603 5807 70797458 7153 6326 4598 Toughness (CD**) 1282 1599 1358 1656 1495 NR NR NR(ft-lbs/in³) Elmendorf B (MD*) 288 216 334 317 194 320 398 297 (grams)Elmendorf B (CD**) 621 566 413 630 664 640 621 527 (grams) PPT Tear(MD*) (lbs.) 6.79 6.18 5.99 6.2 6.5 6.2 6.2 5.3 PPT Tear (CD**) (lbs.)7.44 7.42 6.46 6.8 8.1 7.0 7.5 6.1 Dart Impact A 708 610 354 410 186 412186 164 (grams) Puncture (ft-lbs/in³) 316 349 251 231 256 250 227 237Film Block g. 75 33 87 32 17 11.8 17 22 Film Gradient Density 0.91450.9153 0.9155 0.9205 0.9218 0.9198 0.9201 0.9207 (g/cm³) Film Gauge(low) 0.9 0.9 0.9 0.85 0.8 0.98 0.95 1.05 (mils) Film Gauge (high) 1.21.05 1.1 0.95 1 1.08 1.05 1.15 (mils) *MD = Machine direction **CD =Cross direction NR = Not Recorded

In general, films made from the novel formulated ethylene/α-olefincompositions exhibit good impact and tensile properties, and anespecially good combination of tensile, yield and toughness (e.g.,toughness and dart impact). Further, films from the example resinsexhibited significant improvements over films made from the comparativeresins in a number of key properties.

For example, comparing examples 1 and 2 with comparative example 3, thedata show films produced from the melt blends (examples 1 and 2)exhibited significantly higher values for the following film properties:dart ipact, MD tensile, CD tensile, MD toughness, CD toughness MD ppttear, DC ppt tear, CD Elmendorf tear B, puncture and significantly lowerblock.

Comparing example 4 to comparative example 5, the data show filmsproduced from the in-situ blend (made according to U.S. Ser. No.08/010,958 now abandoned) exhibited significantly higher values for thefollowing film properties: dart impact, MD toughness and CD toughness.

Comparing example 6 to comparative examples 7 (an ethylene/1-octenecopolymer made according to U.S. Ser. No. 07/773,375 now U.S. Pat. No.5,520,612) and 8 (an heterogeneously branched ethylene/1-octenecopolymer), the data show films produced from the in-situ blend (madeaccording to U.S. Ser. No. 08/010,958 now abandoned) exhibitedsignificantly higher values for the following film properties: dartimpact, MD yield, CD yield, MD tensile, CD tensile, CD Elmendorf tear Band puncture and significantly lower block.

We claim:
 1. A fiber made from an ethylene polymer composition, whereinthe composition comprises (A) from about 10 percent (by weight of thetotal composition) to about 95 percent (by weight of the totalcomposition) of at least one homogeneously branched linearethylene/α-olefin interpolymer having: (i) a density from about 0.89grams/cubic centimeter (g/cm³) to about 0.935 g/cm³, (ii) a molecularweight distribution (M_(w)/M_(n)) from about 1.8 to about 2.8, (iii) amelt index (I₂) from about 0.001 grams/10 minutes (g/10 min.) to about10 g/10 min., (iv) no high density fraction, (v) a single melting peakas measured using differential scanning calorimetry, and (vi) a slope ofstrain hardening coefficient greater than or equal to 1.3; and (B) fromabout 5 percent (by weight of the total composition) to about 90 percent(by weight of the total composition) of at least one heterogeneouslybranched ethylene polymer having a density from about 0.93 g/cm³ toabout 0.965 g/cm³.
 2. The fiber of claim 1 wherein the heterogeneouslybranched ethylene polymer is an interpolymer of ethylene with at leastone C₃-C₂₀ α-olefin.
 3. The fiber of claim 1 wherein the homogeneouslybranched linear ethylene/α-olefin interpolymer is an interpolymer ofethylene with at least one C₃-C₂₀ α-olefin.
 4. The fiber of claim 1wherein the homogeneously branched linear ethylene/α-olefin interpolymeris a copolymer of ethylene and a C₃-C₂₀ α-olefin.
 5. The fiber of claim4 wherein the homogeneously branched linear ethylene/α-olefin copolymeris a copolymer of ethylene and 1-octene.
 6. The fiber of claim 2 whereinthe heterogeneously branched ethylene polymer is a copolymer of ethyleneand a C₃-C₂₀ α-olefin.
 7. The fiber of claim 6 wherein theheterogeneously branched ethylene polymer is a copolymer of ethylene and1-octene.
 8. The fiber of claim 1, wherein the at least onehomogeneously branched linear ethylene/α-olefin interpolymer has a slopeof strain hardening coefficient from about 1.3 to about 2.3.
 9. Thefiber of claim 1, wherein the composition comprises more than about 40percent (by weight of the total composition) of at least onehomogeneously branched linear ethylene/α-olefin interpolymer.
 10. Thefiber of claim 1, wherein the density of the at least one homogeneouslybranched linear ethylene/α-olefin interpolymer is in the range fromabout 0.905 g/cm³ to about 0.925 g/cm³ and the I₂ melt index is in therange of from about 0.001 g/10 minutes to less than about 1 g/10minutes.